Polymers are high molecular weight chain-like structures formed by-linking together simple molecular units called monomers. Polymers are substances characterized by their viscosity, color, and softening point. Polymers are used in the manufacture of a wide variety of products, including films, foams, and textiles.
Heat and pressure are applied to monomers, typically in the presence of a catalyst in a polymerization reactor, to prepare polymers in either batch or continuous processes. Continuous processes are somewhat more typical. As a specific example, polymer from a continuous polymerization unit immediately may be supplied to a spinneret for extruding into filaments and subsequent use in various textile products. On the other hand, batch polymer typically is solidified and formed into chips, flake, or powder for subsequent processing.
Defects including gels, voids, and carbon and other solid particles in polymers can result in quality problems in products made from the polymer. Gels are a form of degraded polymer formed in polymerization reactors. Gels are thought to be areas across which the individual polymer chains are bridged and are said therefore to be "cross-linked." Gels in a polymer may cause filaments spun from the polymer to break under tension. Gels lead to brittleness and loss of tensile strength in filaments and show up as broken filaments in yarn. Also, the quality of films made from such a polymer may be compromised. Gels are believed to form in the polymerization reactors. Gels tend to form when the polymerization reactor performance has deteriorated or when a process upset has occurred.
Apparatus and methods previously have been proposed for analysis of defects in molten polymer and in polymeric films and fibers. See, for example, U.S. Pat. Nos. 4,715,717; 4,652,124; and 4,529,306. Methods and apparatus for analyzing molten polymer in a polymer reactor have the drawback that the environment is harsh for sensitive optical and electrical equipment, and can result in equipment failure and less accurate results. Films typically are analyzed after production for gels and other defects that can adversely impact the quality of the film. Analysis of defects in filaments for production of various textile products typically has been accomplished by an operator who examines a short length of spun filament under a microscope.
In particular, polyester filaments typically are examined under ultraviolet illumination. Gels that may be present in polyester polymers fluoresce in the orange/red portion of the visible spectrum of electromagnetic radiation when exposed to ultraviolet radiation. The operator counts the fluorescent gels until a predetermined count or length of filament has been reached. This method is tedious, time consuming, and allows only a minuscule fraction of the polymer to be examined. For example, evaluation of one gram of polymer can take up to 12 hours. Another drawback of this method and prior methods and apparatus for examination and analysis of products from polymer, such as films and fibers, is that a relatively large amount of product may be produced before the reactor operating conditions are corrected.
It would be desirable to provide for sampling and monitoring of a molten polymer stream with a minimum of labor to reduce the time required for inspecting the polymer and to provide for early, accurate, and reliable inspection of significant amounts of polymer. In this manner, the detection and analysis of gels in the reactor output could be used to monitor reactor performance, to indicate whether the reactor needs to be scheduled for maintenance, to provide an indication of the performance of spin pack filter systems in the case of spinning of continuous filaments, and to avoid manufacturing significant quantities of product from polymer having an unacceptable number of defects.